[llvm] [GlobalISel] Check width of APInts in Reassoc PtrAdd combine (PR #84335)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

If you ask for `getIConstantVRegValWithLookThrough` from a s64 register, there is no guarantee that the bitwidth of APInt is 64 bit. If I have some fancy non integral AS with 128bit pointers, why should the offset of `G_PTR_ADD` be 128bit?

The test case is using the pre-legalizer combiner. I bet the real assert was in a bigger input.

https://github.com/llvm/llvm-project/pull/84335